1. Field of the Invention
The invention is directed to a method and apparatus for an excavation support system and, more particularly, to a method and apparatus for supporting the walls of an excavation to prevent a cave-in of the walls defining the excavation.
2. Description of the Prior Art
According to the prior art, a first portion of the trench was dug to a first depth and a trench box or support was assembled in or placed in such first portion. The trench was then dug to its full depth, making the trench approximately twice the depth of the first portion.
To support this additional trench depth, the U.S. Pat. No. 3,212,270 to Benintend issued Oct. 19, 1965 shows the use of plates 12 which slide downwardly along guides made up of flanges such as 20, 22 and 23 affixed to and within the walls of safety cage 11. Because only a single plate 12 can be accommodated by each set of flanges, the trench depth is limited to approximately twice the height of safety cage 11.
In U.S. Pat. No. 4,059,964 issued Nov. 29, 1977 to Pavese, there is shown a sheeting installation frame 71 which installed in the pit to a first depth. Sections 72 are then installed into support frame 71 and hammered downwardly through the undug soil beneath the support. Finally, the remainder of the pit is dug between the extended sections 72 (see FIGS. 9, 10 and 11). The marginal edges of sections 72 overlap so that a complete pit wall is created. Since frame 71 only provides for a single set of sections 72, the depth of the final pit is approximately equal to twice the height of support frame 71.
In Japanese Printed Publication 56-77422, after frame 2 is positioned in the trench mouth and shored up as with supports 3, panels 7 are made to engage channels created by guides 6 and slide downwardly behind the frame 2. Once panels 7 are in place, the remainder of the trench can be dug. Since the guides 6 can only handle one set of panels 7, the trench depth is limited to about twice the height of frame 2 (see FIGS. 6 and 7).
The prior art does not show how a trench can be supported, which trench has a depth a number of times the height of the trench box or shield. The present invention is directed to meet these needs.